The present invention relates to a device for selecting the needles in a knitting machine, particularly for stockings.
Devices are known for selecting the needles in circular knitting machines which, generally, comprise a plurality of overlapping selecting levers, individually pivoted with an intermediate portion thereof to a supporting structure which is positioned alongside the needle-bearing cylinder at a level matching that of the selectors or sub-needles. Each of the selecting levers is oscillatable from a first position, wherein one of their ends is at a level which is intermediate between the heels of the selectors so as to avoid interfering therewith, to a second position, in which this end is at the level of the heels of the selectors, so as to interfere therewith and push the related selectors in an inoperative position.
In a published U.S. Pat. No. 4,471,636, a device of this kind is described wherein the selecting levers are operated by rod-like elements pushed along their own axis by electromagnets controlled by a machine control apparatus.
The activation of the electromagnet causes the rod-like element to engage with the matching selecting lever, making it oscillate, while the disactivation of the electromagnet disengages the rod-like element from the selecting lever, which returns to the preceding position due to the action of return springs.
In another U.S. Pat. No. 06/761,625, filed on Aug. 1, 1985 by the same Applicant, a device is described wherein the selecting levers are actuated by intermediate control elements, individually oscillatable around axes which are perpendicular to the axes of oscillation of the selecting levers. These intermediate control elements have an end with a geometrical profile engageable with a matching profile provided on the end of the selecting lever which engages therewith so that an oscillation of the intermediate control elements causes an oscillation of the selecting levers. Each intermediate control element is actuated by two electromagnets: one for the outward stroke of the oscillation and one for the returning stroke thereof.
These known kinds of devices, though they obtain a needle selection which can be controlled by an electronic machine control apparatus, have proved to be susceptible to further improvement.
In the case of the first device described, in fact, the return time of the selecting levers to the first position is related to the return spring and therefore can be relatively long.
In the case of the first and of the second device, each have overall dimensions which, it would be desirable to further reduce, to obtain a greater number of selections with an equal bulk, or a greater operating speed of the machine with an equal number of obtainable selections. The distance between two consecutive heels is closely related to the distance between the selecting levers and this distance depends in turn on the means employed for the operating thereof; a reduction of the distance between the heels of the selectors would allow to reduce the weight of the selectors to full advantage of the operating speed.